The present invention relates to a ceramic alloy with excellent properties particularly for use as an insert for cutting. More particularly, the invention is related to the type of cutting material which is based essentially on ceramic oxide, that is, principally aluminum oxide to which additions of nitrides or carbonitrides from the groups IV B, V B and VI B of the periodic system have been made to attempt to increase the toughness and the thermal shock resistance.
Ceramic materials based on aluminum oxide have been available for a very long time. The mechanical properties of this class of materials have constantly been improved because of a better understanding of the influence of the microstructure and by improved process technique.
The field of application of these ceramic materials was essentially enlarged when it was found that alloying additives could increase the toughness and the thermal shock resistance of these materials. This effect was principally obtained by addition of titanium carbide in concentrations of 25 to 40 w/o (weight percent). The latter class of materials have been used in milling of steel and cast iron.
However, a serious disadvantage of the latter class of material is that they generally must be sintered under pressure to obtain optimal properties because of their sintering inertia. Consequently, the material can be expensive to produce and the geometry of the produced inserts must be limited to very simple forms.
In spite of their good properties (among others an excellent chemical stability), nitrides have up to now not been often used as alloying additives to ceramic materials. The reason, among other things, is the difficulty in obtaining a material without porosity for materials made with nitride additions of the same magnitude as the carbide addition used in commercial mixed ceramic materials. It is well known that even a very small amount of pores has a very negative influence on the cutting properties of ceramic materials.
Lately, an increased interest in materials of oxide-nitride type has been noticed. Thus, alloys based on nitrides and aluminum-oxide have been investigated by among others Rudy (cf. the Swedish patent application No. 7607895-5 or the corresponding German Pat. No. 2,630,687). The investigated alloys comprised among others: Al.sub.2 O.sub.3 --TiN, Al.sub.2 O.sub.3 --MgO--TiN, Al.sub.2 O.sub.3 --Ti(C,N), Al.sub.2 O.sub.3 --Ti(N,O), Al.sub.2 O.sub.3 --MgO--(Ti,Mo)(C,N), Al.sub.2 O.sub.3 --(Ti,Nb)N, Al.sub.2 O.sub.3 --(Ti,V)N, Al.sub.2 O.sub.3 --MgO--(Ti,Mo,Cr)(C,N), Al.sub.2 O.sub.3 --(Zr,Ti)(N,O), Al.sub.2 O.sub.3 --(Ti,Nb)(N,O), Al.sub.2 O.sub.3 --MgO--Hf(C,N), Al.sub.2 O.sub.3 --Ni--Mo--(Ti,Mo)(C,N), Al.sub.2 O.sub.3 --ZrN, Al.sub.2 O.sub.3 --MgO--(Ti,Cr)(C,N), Al.sub.2 O.sub.3 --(Ti,Cr)(C,N) of different sintering procedures. The best technological properties were obtained for the pressure sintered materials. In turning in steel, where the criterion was the life to breakage, a shorter life was obtained for all variants except TiN--Al.sub.2 O.sub.3 and Al.sub.2 O.sub.3 --MgO(Ti,Mo)(C,N) compared to a commercial material of TiC--Al.sub.2 O.sub.3 -Type. However, TiN--Al.sub.2 O.sub.3 was grouped to a different geometry so a direct comparison cannot be made. The alloy Al.sub.2 O.sub.3 --MgO--(Ti,Mo)(C,N) was comparable with the commercial material.
Among further publications relating to nitride-aluminum-oxide alloys, there is the Japanese publication (Kokai) No. 50-89410 (published July 17, 1975). Among other things, there is disclosed a pressure sintered alloy consisting of 75 v/o (volume percent) Al.sub.2 O.sub.3 and 25 v/o TiN compared with a commercial pressure sintered material consisting of 75 v/o Al.sub.2 O.sub.3 and 25 v/o TiC. In turning of steel (cutting speed 800 m/min) less crater wear and flank wear were obtained and in milling (cutting speed 600 m/min) better crater wear resistance of the Al.sub.2 O.sub.3 --TiN-alloy was obtained compared with the commercial material.
Japanese publication (Kokai) No. 51-5216 (published Jan. 16, 1976) discloses alloys consisting of aluminum oxide and nitride, carbonitride or carbide. Among other alloys, pressure sintered alloys with 70 w/o Al.sub.2 O.sub.3 and 30 w/o of a solid solution of TiN/TiC with m/o (or mole percent): 100/0, 70/30, 50/50, 30/70, 10/90, 0/100 were investigated. In turning (cutting speed 500 m/min), an increasing crater wear resistance was obtained with increasing TiN-concentration, while the flank wear was very much increased when the TiN-concentration exceeded 50 m/o in Ti(C,N), so that the flank wear resistance of the last mentioned alloys was lower than the one of TiC--Al.sub.2 O.sub.3. In milling (cutting speed 500 m/min), better results were obtained for Al.sub.2 O.sub.3 --Ti(C,N), with TiN-concentrations up to 50 m/o in Ti(C,N), compared with TiC--Al.sub.2 O.sub.3. For higher TiN-concentrations, a considerable abrasive wear was obtained.
Also, the Japanese publication (Kokai) No. 51-6109 (published Jan. 19, 1976) concerns sintered alloys of the type aluminum oxide-titanium carbide-titanium nitride and among other alloys pressure sintered Al.sub.2 O.sub.3 --TiC--TiN-alloys with 0.8 v/o Ni have been investigated. The TiC/TiN-ratio was kept constant 50/50 m/o and the fraction TiC/TiN was 0.5, 10, 20, 40, 60, 80, 90 and 100 v/o respectively. In turning of steel the best results, that is the lowest values of flank wear and damages because of breakages, were obtained for TiC/TiN-concentrations between 5 and 80 v/o.
Furthermore, pressure sintered alloys with 55 v/o Al.sub.2 O.sub.3, 5 v/o Ni and 40 v/o TiC-TiN where the TiN-fraction was 0.5, 10, 30, 50, 70, 80, 90, 95 and 100 m/o were investigated. Turning tests in steel gave good results, that is low values of flank wear and damages caused by breakages, for TiN-concentrations between 5 and 95 m/o in TiC/TiN. Solely TiC gave a high frequency of breakages.
Inserts were formed of another seres of pressure sintered alloys with 60 v/o Al.sub.2 O.sub.3 and 40 v/o TiC/TiN (50/50 v/o), to which were added 0, 1, 5, 10, 15, 20 and 25 v/o Ni. These inserts were tested in turning. For 0% Ni, a relatively high value of the frequency of breakages were obtained and for Ni-concentrations exceeding 15 v/o abrasive wear increased strongly.
Japanese publication (Kokai) 52-37913 (published Mar. 24, 1977) involves sintered alloys of the type aluminum oxide-titanium nitride-magnesium oxide. Among other alloys, pressure sintered alloys with 74.5 w/o Al.sub.2 O.sub.3, 0.5 w/o MgO and 25 w/o Ti (C,N) with varying nitrogen concentration of the Ti (C,N)-phase were investigated. In turning tests a strongly increased flank wear was obtained when carbon substituted nitrogen in an amount such as the nitrogen concentration of the Ti(C,N)-phase was below 19.0 w/o. Furthermore pressure sintered alloys with 69.5 w/o Al.sub.2 O.sub.3, 0.5 w/o MgO and 30 w/o Ti (N,O) with varying oxygen concentration of the TiN-phase were investigated. In turning tests a strong decrease of life (the criterion being flank wear of 0.3 mm) was obtained if the N-concentration of the TiN-phase was below 19 w/o. A pressure sintered alloy with 74.5 w/o Al.sub.2 O.sub.3, 0.5 w/o MgO and 25 w/o TiN (N&gt;19.0 w/o) was tested in turning (v=300 m/min) and compared with a commercial pressure sintered mixed ceramic alloy with 70 w/o Al.sub.2 O.sub.3 and 30 w/o TiC. The commercial material obtained a considerably greater flank wear. A pressure sintered alloy with 69.2 w/o Al.sub.2 O.sub.3, 0.3 w/o MgO, 0.5 w/o NiO and 30 w/o TiN (N&gt;19.0 w/o) showed a better flank wear resistance in turning tests, and in milling tests a longer milled length before breakage compared with a commercial material with 70 w/o Al.sub.2 O.sub.3 and 30 w/o TiC.
Thus, in summary, alloys based on aluminum oxide and nitrides or carbonitrides of other metals, principally titanium, are well documented in the patent literature. Any corresponding commercial material or alloys accessible to tests and investigations have up to now not appeared. Thus, the production of the different suggested alloys must have involved great difficulties. Furthermore, the necessity of pressure sintering to obtain optimal properties may have turned out not to be economical